Carbon Dioxide Capture and Mitigation of Carbon Dioxide Emissions

ABSTRACT

The present invention describes methods and systems for extracting, capturing, reducing, storing, sequestering, or disposing of carbon dioxide (CO 2 ), particularly from the air. The CO 2  extraction methods and systems involve the use of chemical processes, mineral sequestration, and solid and liquid sorbents. Methods are also described for extracting and/or capturing CO 2  via condensation on solid surfaces at low temperature.

This patent disclosure contains material that is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosure,as it appears in the U.S. Patent and Trademark Office patent file orrecords, but otherwise reserves any and all copyright rights whatsoever.

All patents, patent applications and publications cited herein arehereby incorporated by reference in their entirety. The disclosures ofthese publications in their entireties are hereby incorporated byreference into this application in order to more fully describe thestate of the art as known to those skilled therein as of the date of theinvention described and claimed herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods and apparatuses forcapturing, sequestering, storing, disposing of, or entraining carbondioxide (CO₂), such as is found in the air and the environment, as wellas for mitigating carbon dioxide emissions. In some aspects of theinvention, the CO₂ obtained by the methods and apparatuses is isolatedand stored or disposed of to keep it from the air.

A serious environmental problem facing the world today is global climatechange, i.e., global warming, which has been linked to the increasedproduction of greenhouse gases, namely, carbon dioxide (CO₂). Growingevidence details the accumulation of greenhouse gases in the air, themost important of which is CO₂, as having an associated role in causingglobal climate warming. Since 2001, CO₂ accounted for over 82% of allgreenhouse gas emissions in the United States. Nearly 60% of CO₂ isemitted by utility or industrial power systems, which are based onfossil fuel combustion. A continuing increase in the greenhouse gas CO₂in the air highlights the need to develop cost effective, reliable andsafe methods of CO₂ (or carbon) sequestration.

In order for carbon-rich fossil fuels, such as coal and natural gas, toremain viable and environmentally acceptable energy sources throughoutthe 21^(st) century and beyond, new technologies that employ capture andsequestration, utilization, or recycling of CO₂ need to be developed atreasonable costs. The sequestration of CO₂ would allow the use ofcarbon-based fuels to meet the world's increased energy demands far intothe future, without further increasing the atmospheric concentration ofCO₂. Additionally, for fossil fuels to maintain their predominance inthe global energy market, the disposal of CO₂ and the elimination of CO₂emissions to the air are ultimate goals for curbing the problem ofglobal warming.

The present invention addresses the pervasive problems of the releaseand presence of excessive amounts of CO₂ in the air and providessolutions to these problems in the form of methods and apparatuses forextracting, capturing and sequestering CO₂ and removing excess CO₂ fromthe air.

SUMMARY OF THE INVENTION

It is a general aspect of the present invention to provide new methodsor processes for extracting, reducing, capturing, disposing of,sequestering, or storing CO₂ or removing excess CO₂ from the air, aswell as new methods and processes for reducing, alleviating, oreliminating CO₂ in the air, and/or the emissions of CO₂ to the air.Another aspect of the invention relates to apparatuses, such as wind orair capture systems, to remove or extract CO₂ from air. As used herein,the term “air” refers to ambient air, rather than emitted gas, such asgas that is emitted from a smoke stack or an exhaust pipe. While thelatter may contain air, it is not typically considered ambient air. Inaccordance with the present invention, extraction of CO₂ from airinvolves source gas, which is at atmospheric temperature, pressure andambient concentration of CO₂.

In accordance with an aspect of this invention, a process involvingacidic pH and elevated temperature for sequestering CO₂ as solidcarbonate materials, e.g., magnesium carbonate, is provided. Suitableacids for this process are those that dissolve magnesium bearingsilicates, such as serpentine, or olivine. The acidic solution formedcontains dissolved magnesium salts, as well as some silica and dissolvediron salts. The acidic solution is neutralized to remove dissolvedsilica, and the dissolved iron salts are precipitated out as iron oxidesand/or hydroxides. According to one aspect of the method, the magnesiumsalts in the solution are transformed into ammonium salts viaprecipitation of magnesium by the addition of ammonia-containingreagents, such as ammonium hydroxide, ammonium carbonate, or ammoniumbicarbonate. Unless otherwise defined, the terms “method” and “process”are used interchangeably throughout this disclosure.

In an aspect of the present invention, a method of extracting orsequestering carbon dioxide is provided. The method comprises (a)dissolving a magnesium bearing silicate in an aqueous acid to form anacidic solution; (b) increasing the pH of the solution of step (a) toprecipitate one or more magnesium components; and (c) carbonating theprecipitated magnesium components from step (b) to bind carbon dioxide.In another aspect the invention provides a method of extracting orsequestering carbon dioxide, comprising: (a) dissolving a magnesiumbearing silicate in an aqueous acid to form an acidic solution; (b)increasing the pH of the solution of step (a) to precipitate one or moremagnesium components; (c) carbonating the precipitated magnesiumcomponents from step (b) to bind carbon dioxide; and (d) recoveringammonia gas and acid by thermal decomposition, e.g., heating, or byelectrodialysis.

In another aspect, the present invention provides a method or process ofextracting, sequestering, or capturing carbon dioxide. The processcomprises (a) dissolving a magnesium bearing silicate in an aqueous acidto form an acidic solution; (b) neutralizing the acidic solution toremove partially-dissolved silica and produce a dissolved magnesiumcomponent; (c) precipitating a solid magnesium component from theneutralized solution with an ammonia containing reagent, therebyproducing an ammonium salt in the solution; (d) precipitating theammonium salt from the solution; and (e) carbonating the precipitatedmagnesium component to sequester or eliminate carbon dioxide, e.g., fromthe air. In addition, ammonia gas and acid (in liquid form) can berecovered in the method by thermal decomposition, e.g., heating, or byelectrochemical methods.

In another aspect, the present invention provides a method ofextracting, sequestering, reducing, or eliminating carbon dioxideinvolving (a) dissolving a magnesium bearing silicate in an aqueous acidto form an acidic solution; (b) neutralizing the acidic solution with aneutralizing agent to precipitate iron and silicate; (c) precipitatingmagnesium from the solution with a base, such as, for example, anammonia-containing reagent; and (d) carbonating the precipitatedmagnesium component from step (c) to extract, sequester, reduce, oreliminate carbon dioxide. In addition, thermal decomposition orelectrochemical processes can be used to recover ammonia and acid. Asused herein, a base is a water-soluble compound, or aqueous solutioncomprised therefrom, that is capable of reacting with an acid to form asalt. Illustratively, such compounds comprise molecules, substances, orions able to take up a proton from an acid, or able to give up anunshared electron pair to an acid. Basic solutions comprising themethods of the invention generally have a pH above about 7.

In another of its aspects, the present invention provides processes forextracting carbon dioxide from the air using solid or liquid sorbentsthat bind CO₂. Examples of solid sorbents include, without limitation,activated carbon, zeolites, or activated alumina. Examples of liquidsorbents include, without limitation, high pH solutions, such as sodiumhydroxide solution, potassium hydroxide solution, or organic solvents,e.g., monoethanolamine (MEA), or SELEXOL®.

In another aspect, the present invention provides a method forextracting or capturing carbon dioxide from air using a solid absorberor sorbent material. The method involves (a) exposing a carbon dioxideabsorber material comprising a large absorption surface to the air untilthe absorber material is saturated, or nearly saturated, with carbondioxide; (b) removing remnant air from the saturated absorber materialunder vacuum or reduced pressure; (c) condensing the carbon dioxide on acold surface to capture the carbon dioxide, e.g., in a solid form; and(d) releasing the captured carbon dioxide to a system for collection,storage, or transport. In accordance with this method, the solid sorbentmaterial can comprise materials, objects, or substances, such as beads,rods, fabric, or moveable objects comprising rough surfaces, that movewhile exposed to air. In one aspect of the method, the carbon dioxidesolid sorbent comprises a material that absorbs CO₂ throughout itsentirety. Such a sorbent is preferably hydrophobic. Alternatively, thecarbon dioxide sorbent comprises an inert material that is coated orcovered with one or more CO₂ sorbents. Further in accordance with themethod of this aspect of the invention, steps (b) and (c) can beperformed in a first and second vacuum chamber, respectively, asdescribed further herein. In addition, absorbed CO₂ can be released andcaptured in condensed form, i.e., dry ice, in a cold trap serving as thecold surface.

In a further aspect, the present invention provides a cryogenic carbondioxide capturing or entrapping system comprising (a) a first chamber,or evacuation chamber, that houses carbon dioxide sorbent material,which is laden with carbon dioxide, for example, or on which carbondioxide is captured; (b) a vacuum system which connects to the firstchamber, partially reduces pressure therein and removes remnant air fromthe sorbent material; and (c) a second chamber which is connected to thefirst chamber and which has a temperature suitable for condensation andcollection of carbon dioxide from the first chamber as solid carbondioxide onto one or more surfaces in the second chamber. For example,the temperature of the second chamber can be about −80° C. or about−100° C. or lower. The second chamber can comprise a reduced partialpressure relative to the first chamber.

In another aspect, a method of sequestering CO₂ in ocean waters isdescribed and involves the calcining of a material, such as limestone,dolomite, or carbonate to capture CO₂ from the air, for ultimatedisposal in the ocean. According to this method, the alkalinity of theocean surface is raised by the introduction (e.g., by injection) ofmetal oxide and/or metal hydroxide-containing materials such as, withoutlimitation, MgO/CaO, Mg(OH)₂/Ca(OH)₂, MgO/CaCO₃, or Mg(OH)₂/CaCO₃. Suchmetal oxide materials are obtained by a calcination process and can leadto the additional capture of two moles of CO₂ for every mole of CO₂entered into the system, as described herein. In this aspect, the CO₂liberated in the calcination process plus the CO₂ resulting from theenergy consumption of the calcination process is captured and disposedof. Accordingly, a method for removing carbon dioxide from air isprovided, involving (a) calcining a metal carbonate—(e.g., calciumcarbonate and/or magnesium carbonate) containing material to obtain oneor more metal hydroxide calcination products; (b) introducing thecalcination products of step (a) into a body of water so that thecalcination products dissolve at or near the water surface; and (c)increasing the alkalinity of the water so as to capture at least twotimes the amount of carbon dioxide that is released by the calcining ofstep (a). After their production, the calcination products of step (b)can be finely dispersed into ocean or seawater from one or more vesselsthat drag behind or between them a line that drops a fine powder in thewater, as described herein. Alternatively as described, the calcinationproducts are fashioned into larger pellets that are dropped or ejectedinto the water. Such pellets can comprise CaCO₃/MgO mixtures anddisperse and dissolve at the water's surface.

In another of its aspects, the present invention provides a method ofcarbon capture that removes CO₂ from air. The method also advantageouslyserves to regenerate the sorbent employed in the method. The methodinvolves the use of an alkaline liquid sorbent, e.g., sodium hydroxide(NaOH)-based, to remove CO₂ from ambient air and produce carbonate ions.The resultant sodium carbonate (Na₂CO₃) solution is mixed or reactedwith calcium hydroxide (Ca(OH)₂) to produce sodium hydroxide and calciumcarbonate (CaCO₃) in a causticizing reaction, which transfers thecarbonate anion from the sodium to the calcium cation. The calciumcarbonate precipitates as calcite, leaving behind a regenerated sodiumhydroxide sorbent, thus regenerating the sorbent. The calciteprecipitate is dried, washed and thermally decomposed to produce lime(CaO) and gaseous CO₂ in a calcination process. Thereafter, the lime ishydrated (slaked) to regenerate the calcium hydroxide sorbent. In arelated aspect, this method can be implemented using air capturingsystems, for example, towers or air or wind capture units of variousdesign, which function as the physical sites where CO₂ is captured andremoved from the air.

In another aspect, the present invention provides a method forextracting or capturing carbon dioxide from air, comprising: (a)exposing air containing carbon dioxide to a solution comprising a base,resulting in a basic solution which absorbs carbon dioxide and producesa carbonate solution; (b) causticizing the carbonate solution with atitanate-containing reagent; (c) increasing the temperature of thesolution generated in step (b) to release carbon dioxide; and (d)hydrating solid components remaining from step (c) to regenerate thebase comprising step (a).

In another aspect, the present invention provides a method forextracting or capturing carbon dioxide from air comprising: (a) exposingair containing carbon dioxide to a solution comprising a base, thusresulting in a basic solution which absorbs carbon dioxide and producesa carbonate solution; (b) causticizing the carbonate solution with acalcium hydroxide containing reagent; (c) calcining the resultingcalcium carbonate under thermal conditions in which one or more mixedsolid oxide membranes is interposed between the combustion gases and theinput air; and (d) hydrating the product lime to regenerate the calciumhydroxide involved in step (b).

In yet another aspect the present invention provides systems andapparatuses for extracting, capturing, removing, or entraining CO₂ fromthe air. Such capture apparatuses can include wind and air capturesystems or a cooling-type tower for extracting, capturing, removing, orentraining CO₂ as further described herein. Fan driven systems are alsoencompassed.

Additional aspects, features and advantages afforded by the presentinvention will be apparent from the detailed description, figures, andexemplification hereinbelow.

DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a schematic depiction of an overview of an airextraction process. Drying (d) and hydrating (h) are not specificallyshown. In accordance with an embodiment of the present invention, such aprocess is functionally integrated into an air capture system.

FIGS. 2A and 2B schematically depict a type of CO₂ capture system thatis adapted to wind flow, e.g., venturi flows. In FIGS. 2A and 2B, thethick black lines represent a solid structure as seen from above. As theair moves through the narrowed passage, the pressure drops (VenturiEffect). As a result the higher pressure air inside the enclosures thatare open to the back of the flow have a tendency to stream into the lowpressure air flow.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to carbon dioxide (CO₂)extraction, reduction, capture, disposal, sequestration, or storage,particularly from the air, and involves new processes and apparatuses toreduce or eliminate CO₂, e.g., greenhouse gas CO₂, from the environment.Both air extraction and mineral sequestration of CO₂ are encompassed bythe invention. The processes and systems described herein are aimed ateffective and efficient carbon management, including cost effectivenessand efficient heat management resulting from the processes. Suchprocesses and systems have been developed to extract or remove CO₂ fromair, where, for example, the CO₂ concentration is approximately 0.037%.Thus, the processes and products of the invention provide useable andeconomically viable technologies for tackling and handling theescalating problem of global warming.

In one embodiment, the present invention encompasses a chemical processfor extracting, reducing, or sequestering CO₂ by generating solidcarbonate minerals, silica and water from basic rock materials andcarbon dioxide. Advantageously, the process can eliminate the energypenalty that can result from other implementations of mineralsequestration. The CO₂ disposal process according to this inventioncombines an alkaline base, for example, in the form of magnesium oxideor hydroxide extracted from peridotite rock, with CO₂ to form stablemagnesium carbonate. The overall chemical process is energy neutral andcan achieve the consumption of only mineral rock and carbon dioxide.

The process according to this embodiment involves dissolving ordigesting magnesium bearing silicate minerals (e.g., peridotite rock),such as serpentine, olivine, etc., at an acidic pH to extract magnesiumions. In acidic solution, magnesium dissolves, as do some of thesilicate and various iron salts; other silicates can also precipitateout in acidic solution. Suitable acids for this process are those thatdissolve peridotite rock, and can be strong or weak acids, asconventionally known in the art. Suitable acids have a pH in the rangeof about pH 4.5 to pH 5 or less, or molar concentrations in excess of0.00001 moles per liter of hydrogen ions. Illustrative examples of acidsfor use in the process include, without limitation, hydrochloric acid,sulfuric acid, ammonium bisulfate, citric acid, chromic acid, phosphoricacid, acetic acid and combinations thereof. Also illustratively, acombination of weaker acids, e.g., orthophosphoric acid and oxalic acid,can be used. The acidic solution that is formed is separated fromundissolved residues using a counterstream washing operation. Forexample, the residues are filtered from the acidic solution and thefiltrate is rinsed with water to remove any acid that is entrained withthe solids.

The pH of the acidic solution is increased using an alkaline reagent orbase. For example the acidic solution is neutralized with an amount ofbase sufficient to raise the solution pH to about 7. As the pH of thesolution is increased, silica and iron hydroxide are precipitated out asiron oxides and/or hydroxides, thus yielding a “brine” solution of amagnesium salt of the acid. After neutralization, the dissolvedmagnesium preferably remains in solution, although the pH of thesolution is close to that at which the Mg salt precipitates, e.g., Mgprecipitates in the form of magnesium hydroxide when the solution pHexceeds about pH 8. Some magnesium salts may be even less soluble. Theneutralized solution, e.g., a clear brine, is then titrated with a basicsolution, such as NaOH, KOH, NH₃, NH₄OH, or carbonates, as nonlimitingexamples. The increase in solution pH results in the precipitation ofthe magnesium component, e.g., Mg(OH)₂. If, for example, the base usedfor titration is a hydroxide, e.g., NaOH, KOH, NH₄OH, the magnesiumprecipitate constitutes an Mg(OH)₂ product, which can be carbonated.Alternatively, if the base is a carbonate, for example, (NH₄)₂CO₃ orNa₂CO₃, then the precipitate is a carbonate, e.g., MgCO₃.

Prior to carbonation, the precipitated magnesium component product,e.g., an Mg(OH)₂ product, can be washed, e.g., using a counterstreamoperation, to remove the salt from the resulting filter cake. Followingthe precipitation of the magnesium component, e.g., Mg(OH)₂, a salt(e.g., NaCl) brine remains and is subsequently processed as describedbelow. More generally, the salt mixture in this aspect is comprised ofthe cation introduced in the titration/precipitation step and the anionintroduced in the above-described first step. The remaining saltpreferably remains in solution, at least until the magnesium component,e.g., Mg(OH)₂, is removed. In one embodiment, the salt in solution isfreed from any dissolved impurities by crystallizing or precipitatingthe impurities from the salt, which preferably stays in solution.

In a specific embodiment, a Mg(OH)₂ or MgCO₃ magnesium component isprecipitated with a base comprising an ammonia-containing reagent.Illustratively, ammonia, ammonium hydroxide, ammonium carbonate, orammonium bicarbonate can serve as ammonia-containing reagents for use inthe process to precipitate a magnesium component, such as Mg(OH)₂ orMgCO₃; the negative ion (anion) from the magnesium salt is thentransferred from the magnesium to the ammonium ion creating ammoniumsalts, e.g., ammonium sulfate, via precipitation by the addition of theammonia base reagent to increase or raise the pH of the acidic solution.

In one embodiment involving the use of an ammonia reagent, a step of theprocess involves increasing the temperature, e.g., by heating, of theammonium salt to recover the ammonia and the acid. The temperature ofheating depends upon the ammonium salt used. In general principle, theammonia salt is heated to relinquish the ammonia gas, leaving behind anacid or anhydride of an acid. For example, to transform a mixture ofammonium sulfate and water into ammonium bisulfate and ammonia, themixture is heated to about 350° C. Heating serves to carbonate solidmagnesium hydroxide or magnesium carbonate with gaseous carbon dioxide.Thus, for example, in one embodiment, the ammonium salt can beprecipitated from the solution by reducing the volume of water. Thereduction in water volume can occur by evaporation, membrane separation,and the like. In another embodiment, the ammonium salt can beprecipitated from the solution by changing the temperature. For example,lowering the solution temperature causes the solubility product to beexceeded. This results in the precipitation of the salt. Lowering of thetemperature can be achieved by allowing the solution to reach roomtemperature, or by other means known to those skilled in the art. Theprecipitated or solid ammonium salt is then heated to a temperaturesufficient to dissociate the particular salt, for example, about 100° C.or greater. This releases free ammonia. Thus, having lost its base, theammonium salt reverts to an acid and comprises an acid that is solid inan anhydrous form, e.g., ammonium bisulfate. The acid and ammonia can berecovered, e.g., by combination with a gas/solid carbonation cycle asdescribed below, or by absorption into water, and the magnesium silicateis converted to silica and magnesium hydroxide.

Another embodiment of the process involves carbonating the precipitatedmagnesium component. Carbonation can occur by bringing together solidmagnesium hydroxide with gaseous carbon dioxide. The two materials reactto form magnesium carbonate and steam in an exothermic reaction, whichcan proceed at elevated temperatures. An advantage of this process isthat the above-described acid/ammonia cycle is combined with a gas/solidcarbonation cycle that provides all or part of the heat for the recoveryof the acid and the ammonia.

After generating a solid magnesium precipitate product, e.g., amagnesium hydroxide product, this product is carbonated at elevatedpressure and temperature, for example, in an autoclave system. In suchsystems, the temperature is typically about 400° C. or 500° C. or above,and the pressure is typically about 1 atmosphere, (ambient pressure), toabout 50 atmospheres or greater. In the process, magnesium hydroxidereacts with gaseous CO₂ in a carbonation cycle. The reaction isexothermic; and with appropriate heat management, for example, the useof suitable heat exchangers and/or the design of a physical plant toallow efficient heat transfer, this heat can be collected and applied tothe recovery of the ammonia and the acid in the method. The heat of thereaction is thus harnessed and utilized. For added efficiency, thesystem embraces a counterstream heating of reactants with the sensibleheat stored in the reaction products. To capture and essentially disposeof CO₂, the ammonia and carbon dioxide cycles can be “tied together” andthe energy in both can be shared. Since the overall reaction isexothermic, this can provide a substantial reduction in the energypenalty incurred by currently-performed mineral carbonation processes.

In another embodiment, the above-described process can include theelectrochemical recovery of ammonia gas and acid, e.g., by the use ofelectrodialysis. For, example, electrochemical recovery comprisesintroducing the salt brine into a dialysis apparatus, for example, aconventional electrodialysis apparatus that separates positive andnegative ions with an applied current, thereby effectively re-creatingthe acid and the base of the above process. The brine can be dilutedprior to dialysis, as a higher dilution typically requires the use ofsmaller electromotive forces. The electromotive force serves to separatethe anions and cations of the salt and to recreate the acid and basefrom which the salt was formed. A more concentrated solution will havemore ions per unit volume and will require more electromotive force toseparate the ions. In general, the stronger the acid and the base, thehigher the pH change that needs to be maintained in the apparatus, whichtypically is comprised of one or more cells, or one or more stacks ofcells to reduce energy demand. The cells are comprised of bipolarmembranes and cationic and anionic membranes, as known to and used byskilled practitioners in the art. For example, in a cell, the bipolarmembrane can be situated between the cationic and anionic membranes.Also, the cationic and anionic membranes can be alternating.

Illustratively, the basic dialysis unit contains one cationic and oneanionic membrane with one bipolar membrane on either end. The bipolarmembrane splits water into hydroxide and hydrogen ions, which allows theacid and base to reform. In addition, hydrogen and oxygen gas areformed. A stack of cells decreases the amounts of these gases that areformed per unit acid/base recovered, and therefore improves theeconomics of the process and system. If the acid is a weak acid, e.g.,oxalic acid, then the acid does not completely disassociate; thus, thepH on the acidic side stays higher, compared with a strong acid, e.g.,HCl. If the positive ion is a weak base, which limits the formation offree OH-ions in the brine, then the pH remains lower than for a strongbase, e.g., NaOH.

When ammonia is involved in the electrodialysis system, the ammonium(NH₄) ion itself dissociates into NH₃ and H⁺, and the NH₃ leaves thesolution as a gas, which can be re-captured and re-used in theabove-described process. As ammonia is a weak base, the use of ammonialimits the pH of the solution such that the pH is not raised as high asby using a stronger base, such as NaOH. In general, the lower the pHdifference between the acid and the base sides of the dialysis system,the lower the electromotive force that is required. Therefore, theenergy penalty is lowered in the process involving electrodialysis.Accordingly, ammonia reagents, such as ammonium oxalate, ammoniumcitrate, ammonium sulfate, ammonium hydroxide, ammonium carbonate, orammonium bisulfate are advantageous in the method described herein. Inaddition, at the end of the dialysis, water can be removed, for example,by the use of osmotic membranes that reduce the water content of thesolution as it leaves the dialysis unit.

In another embodiment related to the above process for extracting orcapturing CO₂ from air, the base can be carbonated prior to itsintroduction into the brine comprising magnesium according to the aboveprocess. For example, sodium hydroxide could be exposed to air andabsorb CO₂ from the ambient air. If this sodium hydroxide is thenintroduced into the process, carbonates would immediately be formed inthe process, prior to the precipitation of magnesium components.

In another embodiment, magnesium hydroxide resulting from theabove-described process is washed to remove residual salt, e.g., sodiumchloride, and is exposed to CO₂ above ambient temperature (e.g., about25° C.) and pressure (about 1 atm or 1 bar) to produce magnesiumcarbonate. In this embodiment, the carbonation reaction can operate atelevated temperatures, for example, from about 300° C. to less thanabout 900° C., or from about 300° C. to about 500° C., and pressures ofabout 1 (i.e., ambient) to 50 atmospheres. Higher pressures andtemperatures are also encompassed, although it is to be appreciated thatthe high cost of pressurization may render higher pressures undesirable.Preferably, the heat content from the reaction products (e.g., steam andmagnesium carbonate) is transferred to the reactants (e.g., CO₂ andmagnesium hydroxide to avoid the loss of the heat of the reaction intothe heating of the reactants. This is accomplished using commerciallyavailable heat exchangers, which are units built specifically to allowtwo materials to transfer heat without physically contacting each other,such as in a car radiator. The reaction can deliver a substantial amountof heat energy if the incoming CO₂ is heated against the outgoing steam.In addition, the gases can be used to transfer heat between the incomingand outgoing solids. For example, if the reactants enter a vessel at itsoperating temperature, then any heat that is generated can be recovered.The heat generated by the reaction vessel, e.g., 68 kJ/mole of CO₂, canbe used to generate steam and/or electricity for further use. Thus, theprocesses as described ideally expend minimal energy to heat thereactants so that this energy is more easily recovered.

In another embodiment, the magnesium carbonate is gently sintered duringthe cool-down process. Sintering reduces the reactivity of a solid;thus, if magnesium carbonate, for example, is sintered, it is lesslikely to dissolve when exposed or subjected to water.

Suitable acids for use in the above-described process for sequestering,reducing, and/or eliminating CO₂ include those that can dissolveserpentine, olivine, or similar magnesium bearing silicates.Illustratively, citric acid, oxalic acid, acetic acid, chromic acid,sulfuric acid, orthophosphoric acid, oxalic acid, ammonium bisulfate andcombinations thereof, are nonlimiting examples of suitable acids for usein the process. Dissolution by the acid should occur in an aqueoussystem, preferably with a high concentration of acid. A suitableconcentration range for the acids comprises, for example and withoutlimitation, from about 0.01 mol/L to about 10 mol/L. The reaction shouldprogress rapidly, for example, in minutes to hours, depending on thestrength of the acid and the fineness of the powder resulting from thedissolution process. For example, dissolution using HCl, an exemplarystrong acid, can occur in 5 minutes or less for a fine powder. For aweaker acid, e.g., citric acid, dissolution can take 5 minutes or longerto several hours. Heat need not be a component of the reaction; however,the smaller the amount of heat released in the process, the moreadvantageous the acid. Illustratively, and without limitation, acid usedfor dissolving or digesting in the methods may be present in an amountthat is about 1% to about 20%, or about 10%, in excess of thestoichiometric amount.

For the above CO₂ sequestration, reduction, and/or elimination process,the magnesium and iron salts of the acids are preferably relativelysoluble in water. The solubility of the ammonia salt is a strongfunction of the temperature, i.e., changing the temperature of thesolution is an efficient way to recover the salt. A suitable precipitateof the ammonium salt is free of water and the anhydrous form of the acidis a solid. In addition, the ammonium salt can comprise ammonia and theanhydrous form of the acid. The lower the temperature of the ammoniarelease, the better the salt is for use in the process. Similarly, toreconstitute the salt, the heat of formation of the ammonia salt ispreferably small. Accordingly, for optimum operating conditions, lowertemperatures and less water in the process result in less energyexpended in carrying out the process.

In an embodiment, the present invention encompasses a method ofextracting or sequestering carbon dioxide, for example, from air,comprising (a) dissolving a magnesium bearing silicate in an aqueousacid to form an acidic solution; (b) increasing the pH of the solutionof step (a) to precipitate one or more magnesium components; and (c)carbonating the precipitated magnesium components from step (b) to bindcarbon dioxide. In another embodiment, the method comprises (d)recovering ammonia gas and acid, e.g., by thermal decomposition or byelectrodialysis. In an embodiment, the method the magnesium bearingsilicate of step (a) comprises peridotite rock, which can be, forexample, serpentine or olivine. In an embodiment, the aqueous acid canbe citric acid, acetic acid, chromic acid, sulfuric acid,orthophosphoric acid, oxalic acid, ammonium bisulfate, or a combinationof two or more thereof. In an embodiment, the pH of the acidic solutionis less than or equal to about pH 4.5. In another embodiment, the methodcan further comprise neutralizing the acidic solution of step (a) with aneutralizing agent to precipitate iron and silicate. In an embodimentiron and silicate are precipitated prior to the precipitation of one ormore magnesium components. In an embodiment, this neutralizing stepcomprises a neutralizing agent, which can be ammonia or magnesiumhydroxide. In an embodiment, the pH of the neutralized solution is lessthan or equal to about pH 8. In an embodiment, increasing the pH in step(b) involves the use of an ammonia-containing reagent; the reagent canbe selected from NaOH, KOH, NH₃, NH₄OH, (NH₄)₂CO₃, NH₄HCO₃, Na₂CO₃, or acombination thereof. In another embodiment, the method can include theuse of a reagent that is carbonated prior to precipitating the one ormore magnesium components in the step of increasing the pH of the acidicsolution. In another embodiment, the ammonia-containing reagent isselected from ammonia, ammonium hydroxide, ammonium carbonate, orammonium bicarbonate. In another embodiment, the reagent that iscarbonated prior to precipitating the one or more magnesium componentsis an ammonia-containing reagent. In other embodiments, the one or moremagnesium components of step (b) is Mg(OH)₂ or Mg(CO)₃. In anembodiment, the one or more precipitated magnesium components iscarbonated in step (c) by thermal decomposition, e.g., heating, whichcan be at a temperature of about 300° C. to less than about 900° C., orabout 300° C. to about 500° C., or carried out in an autoclave underpressure, e.g., at about 1 to about 50 atmospheres or greater. In anembodiment, the method can further comprise, following step (c), (i)washing the precipitated magnesium component to remove residual salt;and (ii) exposing the precipitated and washed magnesium component tocarbon dioxide at elevated temperature and pressure. Elevatedtemperature can be about 300° C. to less than about 900° C., or about300° C. to about 500° C., and the elevated pressure can be about 1 toabout 50 atmospheres. In an embodiment, precipitated magnesium componentin the methods is magnesium hydroxide or magnesium oxide. In anotherembodiment, the method further comprises recovering ammonia gas and acidfollowing step (c) by thermal decomposition, e.g., heating, or byelectrodialysis. In another embodiment of the method, the acid of step(a) is present in an amount at least about 10% in excess of astoichiometric amount for neutralizing magnesium in the magnesiumbearing silicate.

In another embodiment, the present invention embraces a method ofextracting, sequestering, reducing, or eliminating carbon dioxideinvolving (a) dissolving a magnesium bearing silicate in an aqueous acidto form an acidic solution; (b) neutralizing the acidic solution with aneutralizing agent to precipitate iron and silicate; (c) precipitatingmagnesium components, e.g., Mg salt, from the solution with a base, suchas, for example, an ammonia-containing reagent; and (d) carbonating theprecipitated magnesium component from step (c) to sequester, reduce, oreliminate carbon dioxide. In addition, thermal decomposition, e.g.,heating, or electrochemical processes can be used to recover ammonia andacid. In this method the magnesium bearing silicate of step (a) cancomprise peridotite rock, such as serpentine or olivine. Examples ofacids suitable for use in the method include, but are not limited to,citric acid, oxalic acid, orthophosphoric acid, acetic acid, chromicacid, sulfuric acid, or ammonium bisulfate, which can provide an aqueousacidic solution with a pH of about pH −1 to about pH 4.5, or a pH ofless than about 4.5. Suitable yet nonlimiting neutralizing agents foruse in the method include ammonia or magnesium hydroxide, which canprovide a neutralized solution with a pH of near 7 for purposes ofprecipitating out impurities like iron and silicates. Bases other thanMg(OH)₂ or Mg salts can be used to precipitate magnesium from thesolution, as they will drive the solution to pH values from about pH 8-9(e.g., ammonia) to about pH 14 (e.g., NaOH). In addition, the base usedin the method can be an ammonia-containing reagent, e.g., withoutlimitation, NH₄OH, NH₃, (NH₄)₂CO₃, or NH₄HCO₃, or a combination thereof.Other bases can include NaOH, KOH, or Na₂CO₃, or a combination thereof.

In an embodiment, the base of the above step (c) is carbonated prior toprecipitating the one or more magnesium components. In an embodiment,the magnesium component in step (c) is Mg(OH)₂ or Mg(CO)₃. In anembodiment, the precipitating agent is an ammonia-containing reagent,such as, without limitation, ammonia, ammonium hydroxide, ammoniumcarbonate, or ammonium bicarbonate. In another embodiment, followingstep (c) of the method, the precipitated magnesium component is washed,e.g., by flushing the isolated filtrate with water, to remove residualsalt, and the precipitated and washed magnesium component is exposed tocarbon dioxide at an elevated temperature, e.g., about 300° C. to lessthan about 900° C., and pressure, e.g., about 1 to about 50 atmospheres,or greater. Exposure of the magnesium component to carbon dioxide can beperformed in an autoclave or in any other high temperature solidsreactor. In another embodiment, the precipitated magnesium component inthe method is carbonated in step (d) by thermal decomposition, e.g.,heating, for example, at a temperature of about 300° C. to less thanabout 900° C., or about 300° C. to about 500° C., at atmosphericpressure or elevated pressure, such as in an autoclave. In anotherembodiment, electrochemical processes are employed to recover ammoniaand acid.

In another embodiment, a method of CO₂ extraction comprises (a)dissolving a magnesium bearing silicate in an aqueous acid to form anacidic solution; (b) neutralizing the acidic solution to removedissolved silica and produce a dissolved magnesium component; (c)precipitating a solid magnesium component from the neutralized solutionwith an ammonia containing reagent, thereby producing an ammonium saltin the solution; (d) precipitating the ammonium salt from the solution;and (e) carbonating the precipitated magnesium component to extract,sequester, eliminate, or reduce the carbon dioxide. In this embodiment,the magnesium bearing silicate of step (a) can comprise peridotite rock,such as serpentine or olivine. Examples of acids suitable for use in themethod include, but are not limited to, citric acid, oxalic acid,orthophosphoric acid, acetic acid, chromic acid, sulfuric acid, ammoniumbisulfate, or a combination of two or more thereof, which can provide anaqueous acidic solution with a pH from about pH −1 to about pH 4.5, orless than pH 4.5. In some embodiments, the acid of step (a) is typicallypresent in an amount/concentration of about 1% to about 20%, or about10%, in excess of stoichiometric need. In the method, theammonia-containing reagent of step (c) can be ammonia, ammoniumhydroxide, ammonium sulfate, ammonium oxalate, ammonium citrate,ammonium carbonate, or ammonium bisulfate. In one embodiment, theammonia-containing reagent is carbonated prior to precipitating themagnesium component, e.g., Mg(OH)₂. or Mg(CO)₃. In one embodiment,following step (c) of the method, the precipitated magnesium componentis washed to remove residual salt, and the precipitated and washedmagnesium component is exposed to carbon dioxide at an elevatedtemperature, e.g., about 300° C. to less than about 900° C., or about300° C. to about 500° C., and pressure, e.g., about 1 to about 50atmospheres, or greater. In one embodiment, the ammonium salt of step(d) is precipitated by reducing the volume of the solution, e.g., byevaporation or membrane separation. In another embodiment, the ammoniumsalt of step (d) is precipitated by reducing the temperature of thesolution. In one embodiment, the ammonium salt precipitate of step (d)is free of liquid water. In one embodiment, the carbonating step isperformed by temperature elevation, e.g., heating, for example, to atemperature of about 400° C. to about 500° C. or above, at atmosphericor elevated pressure. Elevated pressure, e.g., about 1 to about 50atmospheres or greater, can be achieved, for example, by use of anautoclave. In one embodiment, ammonia and acid can be recoveredfollowing step (e). The recovered acid can be solid and anhydrous. Inone embodiment, the ammonia and acid are recovered by thermaldecomposition. In another embodiment, the ammonia and acid are recoveredthrough the use of electrochemical techniques.

In another embodiment, the invention encompasses a method forextracting, reducing, or sequestering carbon dioxide, which comprises(a) dissolving a magnesium bearing silicate in an aqueous acid to forman acidic solution; (b) increasing the pH of the solution of step (a) toneutralize the acidic solution of step (a); (c) introducing ammoniumcarbonate or ammonium bicarbonate into the solution of step (b) toprecipitate magnesium carbonate or related hydrated forms thereof; and(d) carbonating the ammonia to form ammonium carbonate or bicarbonate soas to bind carbon dioxide. In a related embodiment, ammonia gas and acidare recovered following step (c) and prior to step (d). In anembodiment, the magnesium bearing silicate of step (a) comprisesperidotite rock, which can be serpentine or olivine, for example. In anembodiment, the aqueous acid of step (a) is selected from citric acid,acetic acid, chromic acid, sulfuric acid, orthophosphoric acid, oxalicacid, ammonium bisulfate, or a combination of two or more thereof. In anembodiment, the pH of the acidic solution is less than or equal to aboutpH 4.5. In an embodiment, the iron and silicate precipitate in theneutralized solution of step (b) and prior to precipitation of magnesiumcarbonate or its related hydrated forms. In an embodiment of the method,the pH is increased using a neutralizing agent selected from ammonia ormagnesium hydroxide; in an embodiment, the pH of the neutralizedsolution is less than or equal to about pH 8. In an embodiment,increasing the pH in step (b) comprises an ammonia-containing reagent,which can be one or more of NaOH, KOH, NH₃, NH₄OH, (NH₄)₂CO₃, NH₄HCO₃,Na₂CO₃, or a combination thereof. In an embodiment, theammonia-containing reagent is selected from ammonia, ammonium hydroxide,ammonium carbonate, or ammonium bicarbonate.

In another embodiment, the present invention embraces a method ofextracting, sequestering, reducing, or eliminating CO₂ from the airusing solid sorbents. In this embodiment, CO₂ can be extracted orcaptured directly from the air using the solid sorbents. Thereafter, thesorbent is recycled and the captured CO₂ is recovered in a pressurizedstream of concentrated, nearly pure CO₂. Solid materials having a highaffinity to CO₂ can absorb CO₂ even at the low partial pressures asfound in air. In accordance with this embodiment, the solid sorbentmaterial is exposed to air. Suitable absorbers or sorbents for use inthe method include, without limitation, easily-handled small objects,such as, for example, beads or rods that move along surfaces exposed tothe air. Such objects serve as collection surfaces and need not be ofany particular shape or size, but are exposed to air that flows overand/or around and/or through them. Alternatives to beads or rods includeabsorber materials that can be fashioned into fabric-like materials thatare exposed to the air and absorb the CO₂, or a fraction thereof, thatis present. Other alternative materials include small boards with roughsurfaces that are attached to wheels rolling down a track, for example.It will suffice for the suitability of the absorber (sorbent) that aircan reach the absorber surface(s) and CO₂ can be bound, either looselyor tightly to the CO₂ sorbent.

Absorber materials can be solid sorbents, i.e., the entire material issorbent throughout. Alternatively, the absorber material can comprise aninert material of which one or more surfaces are coated with one or moresorbents. In either case, a large amount of absorption surface isintended. After exposure to a CO₂ source, the sorbent surfaces becomesaturated with carbon dioxide and cease taking up carbon dioxide. Apreferred sorbent material is one that takes up CO₂ under ambientconditions, and releases a substantial fraction (e.g., in excess of 10%)of the CO₂ at pressures that are not significantly lower than ambientpressure. The sorbent material is preferably inert, apart from itsaffinity to bind CO₂. In addition, the absorber may or may not absorbwater; it is desirable that the absorber does not absorb water.Alternatively, at least the CO₂ will quantitatively displace water fromthe binding surface of the sorbent material. If the solid sorbentmaterial absorbs water, it is preferable that it does not release waterin the recycle step of the method described below, because (i) thematerial has been displaced by CO₂, and thus is not present in therecycle loop; (ii) it has bound tightly enough to remain attached to thesorbent; and/or (iii) the water vapor pressure in the recovery cycle issufficiently high to prevent the freeing of water. Should water absorbonto the sorbent and displace CO₂, more energy is consumed in theprocess; this is not a particularly desirable result. Thus, the sorbentmaterial should be less attractive to water than it is to CO₂ so thatCO₂ absorption is not reduced, or so that CO₂ is not released duringsublimation.

Illustrative and nonlimiting examples of solid sorbent materials for usein the methods of this invention include hydrophobic carbon compoundsthat absorb CO₂ from the air (Oak Ridge National Laboratory, Oak Ridge,Tenn.), activated carbon (amorphous carbon solids, often from naturalbiomass sources), molecular sieve carbon (MSC) (fossil fuel, e.g., coal,petroleum), carbon fiber composite molecular sieves (CFCMS), formed byjoining petroleum pitch-derived carbon fibers with a phenolicresin-derived binder to form a monolithic, highly porous carbon filter“cake”, activated alumina, and natural (“mineral”) and syntheticzeolites, or specialized zeolites, such as silicalites. Zeolites caninclude, for example, A, X, Y, or mordenite, etc. which tend to possessthe physico-chemical properties that allow them to bind CO₂. Otherzeolites, such as those having a high Si/Al ratio, such as silicalite,tend to be more stable to hydrothermal treatments and have less affinityto water. Such materials can be hydrophobic and could serve as CO₂capturing agents that are not affected by the presence of water vapor.Other useful zeolites are those having a high sodium content combinedwith a medium Si/Al ratio. In addition, suitable solid sorbents offerseveral advantages, including low binding energy, high stability,selectivity, high absorption capacity, kinetic advantages, andsimplicity of system design.

In another embodiment, a cryogenic pressure system is embraced toperform the CO₂ capture, sequestration, reduction, or eliminationmethods of this invention. In accordance with this embodiment, theCO₂-saturated sorbent material is packed into a first chamber at roomtemperature that can be evacuated. The first chamber can be connected toa low-grade vacuum system that removes remnant air that is caught in oron the sorbent material. After a pressure reduction in the first chamberfrom atmospheric pressure to near vacuum pressure, CO₂ is allowed toflow from the sorbent into a second chamber where the CO₂ condenses ontocold surfaces (e.g., solid substrates) as solid carbon dioxide. CO₂ flowcan be controlled by the opening of a valve or another means thatachieves the desired result. The pressure in the second chamber is lowerthan the vapor pressure of CO₂ in the first chamber, and can depend uponthe type of absorbent material that is utilized in the second chamber.At sufficiently low temperature, any surface material is suitable forthe purpose of this method.

Illustratively, the pressure of the second chamber can be about 100 ppmof an atmosphere, or about 0.001 psi. The temperature in this secondchamber is low enough for the CO₂ to condense out, e.g., in the form ofdry ice. Accordingly, the temperature is about −80° C. or −100° C. orlower. Liquified air may be used as a coolant. Without wishing to bebound by theory, because the temperature in the second chamber is belowthe freezing point of CO₂, the equilibrium partial pressure of CO₂ inthe second chamber is far lower than the pressure of CO₂ over thesaturated (warmer) CO₂ sorbent surfaces in the first chamber. As aconsequence, the system establishes a pressure gradient between the twochambers and the CO₂ travels from the chamber having higher pressure tothe chamber having lower pressure chamber until enough CO₂ has beenremoved from the sorbent so that the partial pressure in the firstsorbent chamber has dropped as well. When a substantial amount of carbondioxide has formed as dry ice on the solid surface(s), which serve as a“cold trap” within the second chamber, the collected dry ice is confinedto a small volume and brought to ambient temperature. As the dry icewarms up, it turns into CO₂ gas, which, as it is confined to a smallvolume, will be produced at a high pressure. This gas is then releasedunder pressure from the cryogenic system, e.g., into containment vesselsand the like, for further storage or collection.

In this embodiment, the partial pressure of CO₂ is reduced over thesystem to the point that a substantial fraction of the adsorbed CO₂ isreleased and captured in the cold trap. The dry ice that forms in thecold trap is collected over time, e.g., from about 15 minutes to severalhours, or from about 20 minutes to one hour. For example, the rate ofheat transfer between the cold trap and the solid sorbent in the secondchamber can be as fast as about 50 g/m²/sec. Thus, a system containing 1ton of sorbent containing about 50 kg of CO₂ could release its CO₂ asdry ice in about 20 minutes. When sufficient amounts of dry ice areavailable, the dry ice is confined to a small volume, e.g., by scrapingit from the cold trap and moving it to a suitably sized vessel. The sizeof the vessel is such that when the solid CO₂ is allowed to warm or heatto ambient conditions, it is then at the desired pressure. The CO₂ isthen released under pressure, e.g., about 60 to about 200 bar pressure,to a suitable or desired CO₂ containment vessel, or handling, storage,or transportation system. Advantageously, such a vacuum systemeffectively requires no pumps to pressurize gaseous CO₂. By keeping theCO₂ confined, pressure is obtained from the energy input that wasprovided in the refrigeration system that maintained a low temperaturein the cold trap.

In another embodiment, the present invention embraces a systemcomprising a solid sorbent for CO₂ capture comprising impregnatedsupport matrices or substrates, e.g., cloth materials, to transportsolid particles into and out of an air stream. This system removescarbon dioxide from the atmosphere in a manner akin to that of a windcapture device. The support matrix provides a means of moving the solidsorbent into and out of the air stream, similar to the operation of aconveyor belt. The air stream can be air, or a flue gas, or essentiallyany substance, material, or matter that comprises CO₂. In an embodiment,the solid sorbents are mounted or made to adhere to a solid matrix orsubstrate, such as a cloth material, which is then placed on a movingsystem, e.g., a clothesline-type system, to move the matrix or substrateinto the air stream, e.g., wind, and back again.

In another embodiment, particulates are used inside a chamber (orcontainer) followed by air filtration systems that recaptureparticulates from the stream. The system according to this embodiment issimilar to a fluidized bed. One or more solid sorbents can be placedinto a moving gas stream, air or flue gas, where the sorbent “floats”around while absorbing CO₂. After a specified period of time the sorbentis removed and the absorbed CO₂ is stripped therefrom, for example, bydiverting the gas stream through a second chamber (or container).Accordingly, one chamber (or container) absorbs while the second chamber(or container) is being recycled without release of the particulates tothe environment.

In another embodiment, the present invention embraces methods andsystems for extracting CO₂ from the air using liquid sorbents.Accordingly, the invention provides a method of carbon capture thatremoves CO₂ from air using solid oxide membrane and liquid sorbents.Suitable sorbents include basic solutions, such as sodium hydroxide(NaOH) or potassium hydroxide (KOH), and other often viscous fluids,which are typically caustic. More specifically, the method involves theuse of a hydroxide-based, alkaline liquid sorbent, e.g., NaOH solutionsand the like, to absorb and remove CO₂ from ambient air and producecarbonate ions. The resultant sodium carbonate (Na₂CO₃) solution ismixed or reacted with calcium hydroxide (Ca(OH)₂) to produce sodiumhydroxide and calcium carbonate (CaCO₃) in a causticizing reaction,which transfers the carbonate anion from the sodium to the calciumcation. The calcium carbonate precipitates as calcite, leaving behind aregenerated sodium hydroxide sorbent, thus, regenerating the sorbent.The calcite precipitate is dried, washed and thermally decomposed toproduce lime (CaO) in a calcination process. The thermal decompositionis preferably performed to avoid mixing the CO₂ resulting form thecombustion process, providing the heat with ambient air. This embodimentuses solid oxide membranes to separate input air from the combustionprocess. Oxygen at elevated temperatures can pass through thesemembranes. After calcination, the lime is hydrated in a slaking process.In a related embodiment, this method can be implemented using aircapturing systems, for example, towers or air capture units of variousdesign, which function as the physical sites where CO₂ is captured andremoved from the air.

In yet another embodiment, the resultant NaOH is recycled using sodiumtri-titanate rather than calcium hydroxide. In this embodiment, thereaction occurs in a molten rather than in an aqueous state. As aresult, the absorption solution is highly caustic in order to minimizethe amount of water evaporation required. In another embodiment, theinvention encompasses a method for capturing carbon dioxide from air,comprising (a) exposing air containing carbon dioxide to a solutioncomprising a base resulting in a basic solution which absorbs carbondioxide and produces a carbonate solution; (b) causticizing thecarbonate solution with a titanate containing reagent; (c) increasingthe temperature of the solution generated in step (b) to release carbondioxide; and (d) hydrating solid components remaining from step (c) toregenerate the base comprising step (a). In one embodiment of thismethod, the base of step (a) is selected from sodium hydroxide, calciumhydroxide, or potassium hydroxide. In another embodiment, the carbonatesolution of step (a) of the method is a sodium carbonate (Na₂CO₃)solution. In another embodiment of the method, the solution of step (a)is causticized with sodium tri-titanate.

In related embodiments, the present invention provides systems andapparatuses for extracting, capturing, or entraining CO₂ from the air orwind. Such capture apparatuses can include a wind capture system or acooling-type tower for extracting, sequestering, or capturing CO₂ asfurther described herein. Fan driven systems are encompassed. Windcapture systems refer to freestanding objects similar in scale to a windenergy turbine. For example, such devices contain a pivot that ensuresthat contacting surface can follow the wind directions. The device canoperate with either liquid or solid CO₂ sorbents. A liquid based systemoperates using pumps at the base, which pump sorbent to the top of thedevice. Once at the top, the sorbent flows under gravity back to thebottom via a circulation system. The circulation system can encompasstroughs or other flow channels that expose the sorbent to air.Alternatively, the system could be vertical wires on which sorbent flowsfrom top to bottom. The device is sized such that the sorbent issaturated in one pass. A solid system contains moving components onwhich one or more solid sorbent is bound. These components aremechanically raised into the wind so as to absorb CO₂. Once saturated,the components are removed from the wind stream, isolated and strippedof CO₂. In another embodiment, a cooling tower contains a CO₂ removalzone in the air inlet at the base, which may contain either solid orliquid sorbents in a manner described above.

In another embodiment, a CO₂ capture system according to this inventioncan comprise filter systems wetted by a flow of sodium hydroxide thatreadily absorbs CO₂ from the air, and in the process, converts it tosodium carbonate. Without wishing to be bound by theory, if the pressuredrop across the system due to viscous drag is comparable to the kineticenergy density in the air, then the fraction of CO₂ removed from theflow stream becomes significant, so long as the sorbent materials arestrong absorbers. This is because the momentum transfer to the wallfollows essentially the same physical laws of diffusion as the carbondioxide transfer. In a cooling tower type of system, intake air ispulled through a filter system that is continuously wetted with sodiumhydroxide. Another type of system can involve a slight pressure dropgenerated by other means. In yet another system, air contacts sorbentsurfaces simply by the wind (or moving air) passing through the deviceor system. It will be appreciated that in the design of a contactsystem, the rate of absorption should be considered. In this regard, thevolume of sorbent per unit output of CO₂ is independent of the specificdetails of the air contacting design.

Advantageously, air extraction of CO₂ and systems for this purpose canbe sited based on site-specific conditions, which can includetemperature, wind, renewable energy potential, proximity to natural gas,proximity to sequestration site(s) and proximity to enhanced oilrecovery site(s). The system should be designed for ease of relocation.For example, the extractor may be sited at an oil field in order tominimize transport. In such a case, oil could be reformed and used inthe calcination system.

In other embodiments, chemical processes, e.g., calcinations andcalcining carbonate, are encompassed for the recovery of CO₂. Oneprocess involves oxygen blown calcinations of limestone with internalCO₂ capture. Such calcinations are carried out in a calcining furnacethat uses oxygen rather than air. The use of oxygen results in theproduct stream including only CO₂ and H₂O, which can be easilyseparated. In addition, power plant and air capture sorbent recovery canbe integrated into one facility. Another process involves electricallyheated calcinations. Yet another process involves solid oxide ionicmembranes and solid oxide fuel cell (SOFC)-based separation processes(e.g., Example 2). Another chemical process involves the electrochemicalseparation of CO₂ from Na₂CO₃, for example, using a three-chamberelectrolytic cell containing one cationic membrane and an anionicmembrane. The cationic membrane is located between the central cell andthe negative electrode while the anionic membrane is located between thecenter and the cathode. A current is applied to the cell and then sodiumcarbonate is introduced into the center cell. The ions move toward theopposite electrode. Hydrogen is evolved at the anode and oxygen gas isevolved at the cathode, resulting in the formation of NaOH at the anodeand carbon dioxide gas at the cathode. Several cells can be stackedtogether by placing a bipolar membrane at the electrode locations of thesingle cell. This serves to reduce the amount of gas evolved per unitreagent regenerated.

The present invention embraces remote CO₂ sequestration sites via aircapture. Such remote sequestration following the capture of CO₂ from aircan include ocean disposal from floating platforms or mineralsequestration in territories or environments having the appropriatemineral sites and deposits. The capture of CO₂ from air allows CO₂ to bedisposed of in remote areas that otherwise would be inaccessible to CO₂disposal due to the prohibitively high cost of transporting CO₂ toremote locations.

The present invention further encompasses CO₂ extraction from the oceanusing limestone and dolomite as sources of alkalinity. If provided withsufficient alkalinity, the ocean can remove carbon dioxide from the air.According to this embodiment, ocean disposal can be improved bycalcining limestone or dolomite to capture CO₂ from the air. During thisprocess, CO₂ is released to the air, but the resulting CO₂ uptake isnearly twice as large as the initial CO₂ emission. Thus, a metalhydroxide, e.g., magnesium or calcium hydroxide, dissolved into thesurface of the ocean will raise the alkalinity of the water leading tothe additional capture of two moles of CO₂ for every mole of CO₂ enteredinto the system. Illustratively, and without limitation, in solid form,an ion, such as a calcium ion, Ca⁺², can trap one CO₂ molecule in theform of CaCO₃. However, in dissolved form, the same ion can trap two CO₂molecules as bicarbonate ions (HCO₃ ⁻). Therefore, limestone that isheated (calcined) as described herein releases one CO₂ molecule, butwhen it is dissolved in the ocean, two bicarbonate ions are trapped. Inthis embodiment, the CO₂ that is dissolved in the mixed layer at the topof the ocean is kept in solution by the addition of calcium or magnesiumions. The mixed layer typically, but not necessarily, reaches a depth ofapproximately 100 m. Suitable sources of metal hydroxides include,without limitation, limestone, dolomite, or smaller deposits ofmagnesium carbonates. Although calcium carbonate is supersaturated insea water and is thus difficult to dissolve, sea water is still farbelow the point at which calcium carbonate spontaneously precipitatesout, thereby allowing for some increase in carbonate and/or calcium inthe surface waters of the ocean. Further, the total dissolved calcium inthe ocean is a quite large amount; therefore, the ocean is generallyinsensitive to additions that could allow for substantial increases instored CO₂. Magnesium carbonate also dissolves in sea water, but at aslower rate than does calcium carbonate. Also, the slow dissolution ofmagnesium carbonate can raise the carbonate ion concentration of seawater, which may be counterproductive to dissolving additionalcarbonate. Because added calcium ions disperse relatively rapidly uponexposure to the ocean surface, this can prevent a risk of precipitationof calcium carbonate into the ocean waters.

More specifically regarding this embodiment, a method is provided tointroduce alkalinity into the water as one or more metal hydroxides,e.g., without limitation, MgO/CaO; Mg(OH)₂/Ca(OH)₂; MgO/CaCO₃; orMg(OH)₂/CaCO₃, or a combination thereof. These metal hydroxides arecalcination products obtained by calcining a suitable starting calciumcarbonate- or magnesium carbonate-containing material, e.g., dolomite,limestone, or magnesite, at a temperature above about 400° C., or aboveabout 900° C. The resulting carbon dioxide is captured and sequesteredat the calcination site. For dolomite at a temperature above about 400°C., the CaO component is not calcined, while MgO is calcined at thisrelatively lower temperature. Calcination can be performed byconventional methods (e.g., Boynton, R. S., 1966, Chemistry andTechnology of Lime and Limestone, Interscience Publishers, New York, pp.3, 255, 258), or by using another energy source, such as solar energy,wind energy, electrical energy, nuclear energy, remote sites withunusable methane, etc. According to this method, the calcination productis finely dispersed into ocean or sea water by various procedures. Forexample, introduction into the water can occur from one or more ships orvessels that drag behind or between them a line that drops fine powderin the water. The size of the line is long enough so that localconcentrations of the material are not driven very high. Alternatively,the calcination products can be fashioned into larger pellets, asconventionally known in the art. The pellets are dropped or ejected intothe water, dissolve slowly and distribute the material relativelyuniformly over a larger area as they drift along. Pellets should containsufficient amounts of air, e.g., have sufficient air pockets, to float.Such pellets can advantageously be added to the water in largerquantities versus a fine dispersion. Of particular interest are pelletscomprising CaCO₃/MgO mixtures. By the practice of this method, the netCO₂ balance is positive, even if the CO₂ from the calcination is notcaptured. Notwithstanding, for every CO₂ molecule released by thismethod, nearly two CO₂ molecules are absorbed into the ocean, whichtakes up CO₂ from distributed sources.

In another embodiment, the present invention relates to methods oftransitioning from today's energy system comprising unsequestered CO₂resulting from the use of fossil fuels to the capture and disposal ofCO₂, and ultimately, to renewable energy with recycling of CO₂. Suchtransitioning methods comprise combining CO₂ capture with magnesiumsilicate disposal. In this embodiment, CO₂ can be removed from the air,but rather than disposing of the removed CO₂, it is used as a feedstockfor making new fuel. The energy for the fuel derives from a renewableenergy source or any other suitable source of energy that does notinvolve fossil fuels, such as hydroelectricity, nuclear energy. Forexample, CO₂ is initially collected and disposed of or sequestered inunderground deposits (such as in enhanced oil recovery, (EOR)) or inmineral sequestration. In this way, the source of the energy is fossilfuel that can be extracted from the ground. To maintain anenvironmentally acceptable material balance, the carbon must bere-sequestered or disposed of. Alternatively, carbon can be recycled asan energy carrier. Hydrocarbon, i.e., reduced carbon, contains energythat is removed by the consumer by oxidizing the carbon and thehydrogen, resulting in CO₂ and water. The capture of CO₂ from air allowsthe CO₂ to be recovered; thereafter, renewable energy can be used toconvert the CO₂ (and water) back into a new hydrocarbon. The productionof hydrocarbon can include a number of processes. Illustratively,Fischer Tropsch reactions are conventionally used to convert carbonmonoxide and hydrogen to liquid fuels, such as diesel and gasoline(e.g., Horvath I. T., Encyclopedia of Catalysis, Vol. 2, WileyInterscience, p. 42). Similar methods using CO₂ and hydrogen are alsoestablished. Hydrocarbon can be produced from CO₂ and hydrogen.Hydrocarbon production typically involves the use of energy, e.g.,electric energy, to convert water into hydrogen and oxygen, or CO₂ intoCO and oxygen. Thereafter, fuels such as methanol, diesel, gasoline,dimethyl-ether (DME), etc. can be made.

In other embodiments of this invention, CO₂ capture apparatuses andsystems are encompassed, especially for use in connection with thedescribed processes. In one embodiment, a wind capture system comprisesa CO₂ capture apparatus in which the air delivery system relies onnatural wind flow. Such a CO₂ capture apparatus can be situated in thesame or similar areas to those in which wind turbines are employed. Inanother embodiment, the invention embraces a water spray tower CO₂capture apparatus comprising a cylindrical tower, e.g., approximately100 feet in height, which is open to the air at its top and containsground level exit vents. A vertical pipe comprises the center of thetower through which water can be pumped; the pipe can be capped with anozzle that sprays water horizontally. Water is pumped to the top andsprayed into the air. The resultant evaporation creates a pocket of airthat is colder and denser than the air below it. This leads to a downdraft which forces air through the exit vents. The exit vents contain asolid or liquid sorbent for CO₂ capture. In another embodiment, theinvention embraces an air convection tower CO₂ capture apparatuscomprising a vertical cylindrical tower that is attached to a glassskirt situated approximately 1 foot above the ground level. The glassinsulates the air between the ground and itself, which raises the airtemperature. The hot air then exits through the central tower. A solidor liquid CO₂ capture device is contained in the tower. In anotherembodiment, the invention encompasses a CO₂ capture apparatus comprisinga glass covered slope, which comprises a glass sheet situated somedistance above ground level, e.g., between 0.3 m and 30 m, depending onthe size of the overall apparatus. The glass acts as an insulator thatcauses the air to heat in the sunshine and this results in a draft upthe hill. The resulting flow is guided over CO₂ absorber surfaces, whichremoves CO₂ from the air passing through it. In another embodiment, theinvention encompasses cooling towers to replace a conventional watercooling liquid with a liquid sorbent. The liquid sorbent evaporateswater; in addition, the liquid sorbent collects CO₂ in concentratedform. In all cases, the saturated sorbent is stripped of its CO₂ asdescribed herein.

In another embodiment, wind funneling devices are optimized forthroughput rather than air speed, thereby leading to optimization forCO₂ capture and sequestration. For example, air convection towersemployed for CO₂ capture can be shorter than towers designed forelectricity production, since increased height to promote air speed isnot a requisite for CO₂ sequestration. Further, in such CO₂ captureapparatuses, textile membranes are used to separate alkaline fluids fromthe open air. Such membranes comprise cloth-type fabrics that allow airpassage while limiting sorbent loss through spray. An illustrative, yetnonlimiting, fabric is Amoco 2019. Other CO₂ capture systems includethose that are adapted to wind flow, e.g., venturi flows that createsuction on a set of filters that are balanced by adjusting the size ofthe openings so as to maintain constant flow speed through thefiltration system. As an example, FIG. 2 shows a solid structure (blacklines) seen from above. As the air moves through the narrowed passage,the pressure drops (Venturi Effect). As a result, the higher pressureair inside the enclosures that are open to the back of the flow willhave a tendency to stream into the low pressure air flow. Openings arepreferably large in a high speed wind and small in a low speed wind inorder to maintain a constant pressure drop across the filter system andthus optimize the efficiency of the collector even in the face ofvariable wind speeds. By adjusting the size of the opening, e.g., usingshutters, baffles, etc., one can control the pressure drop across thefilter and can control the amount of air that emerges for optimized flowrates.

It will be appreciated that fans can comprise fan driven CO₂ captureapparatuses and systems, e.g., in CO₂ capture systems at the site of anoil well to perform EOR. The use of a fan or forced air system ensures aspecified air throughput, rather than having to rely on the fluctuationsof natural wind. By creating a constant air flow, a specified productioncan be achieved which may be desirable for production schemes thatrequire constant carbon dioxide output rates. The price for such anarrangement is higher energy cost and capital cost in the installationand operation of fans.

The examples described below are provided to illustrate aspects of thepresent invention and are not intended to limit the invention.

EXAMPLE 1 Capturing CO₂ Directly from the Atmosphere

Alkaline Sodium Sorbents: Removal of a gaseous component through contactwith a liquid is known as wet scrubbing. Wet scrubbing can be dividedinto processes where there is a chemical reaction between the sorbateand the sorbent and where the sorbate is physically dissolved into thesorbent solution. For the air extraction process, an alkaline sodiumsolvent is embraced which reacts chemically with the entrained CO₂. Thechemical reaction for this process is shown below as reaction (1):2NaOH_((aq))+CO_(2(g))→Na₂CO_(3(aq))+H₂O;  (1)

The aqueous carbonate reaction can be simplified by omitting the cation,resulting in the following ionic reaction:2OH⁻ _((aq))+CO_(2(g))→CO₃ ²⁻ _((aq))+H₂O_((l))  (2)ΔG°=−56.1 kJ/mol (ΔH°=−109.4 kJ/mol)

It is noted that the enthalpy and free energy of the reaction are for anominal 1 molar solution. The thermodynamic data, given at 298K and apressure of 1 bar, was obtained from the available literature (Lide D.R., editor in chief, CRC Handbook of Chemistry and Physics 81^(st) Ed.,CRC Press LLC, Boca Raton Fla. (2000)). As a comparison, the free energyof mixing CO₂ with nitrogen and oxygen to form ambient air is given byΔG=RT ln(P _(atm) /P _(CO2))˜20 kJ/mol.  (3)

Accordingly, sodium hydroxide provides a sufficient driving force toeffectively collect CO₂ from ambient air. Even though a lower bindingenergy might be desirable, the high binding energy of chemical sorbentsproves useful in absorbing CO₂ from streams with low partial pressuresof CO₂ As an alternative with a weaker binding energy, sodium orpotassium carbonate buffer solutions can be used as sorbents. In thiscase the absorption can be described by:CO_(2(g))+CO₃ ²⁻+H₂O_((l))→2HCO₃ ⁻  (4)ΔG°=−14.3 kJ/mol (ΔH°=−27.6 kJ/mol)

Even in this case a sufficient thermodynamic driving force is availableto remove CO₂ from the air. For a two molar solution of bicarbonateions, the free energy of the reaction from ambient air is negative ifthe bicarbonate concentration stays below 0.15 molar. A similar resultcan be obtained by calculating the mass action equilibrium usingempirical values for the equilibrium constants. Reaction (4) iseffectively trimolecular and is the result of a sequence of reactionswhich have fast kinetics at high temperatures or very high carbonate tobi-carbonate ratios. Otherwise the process occurs in the diffusionregime, which is much slower, making this reaction kinetically limitedfor air extraction.

According to the present method, chemical decomposition of the resultingsodium carbonate is achieved using calcium hydroxide as an intermediary.A sodium hydroxide solution provides a liquid sorbent that is far moreeasily cycled through a piping system than a calcium hydroxidesuspension. Its binding energy is strong enough and its reactionkinetics fast enough to obviate the need for heating, cooling, orpressurizing the air.

Because CO₂ is so dilute, any such action would result in an excessiveenergy penalty. The hydroxide solution avoids all such complications.Since sodium hydroxide is cheaper than potassium hydroxide, the startingpoint for the air extraction design will be based on sodium hydroxide.

Generally in wet scrubbing, transport resistance is considered tocomprise two distinct components, air side resistance and liquid sideresistance. The air side resistance is dominated by the diffusionbarrier in the laminar boundary layer. Typically, such a boundary layeralso exists on the liquid side. In the bulk fluid, dissolved CO₂ reactswith water, or hydroxide ions to form carbonate or bicarbonate ions. Incontrast to the reactions of CO₂ with water, the reactions withhydroxide reactions are very fast and their reaction time can beignored. However, since diffusion coefficients of CO₂ in air are roughlyfour orders of magnitude larger than ionic diffusion coefficients inwater, it is easy to become rate limited on the liquid side. Avoidanceof liquid side rate limitations is the goal of a good design.

For a one molar carbonate ion concentration in the liquid, theconcentration ratio between carbonate ions in the fluid and CO₂molecules in the gas is 66,000:1. Thus, it will take time to fill up aboundary layer on the liquid side. This suggests that at sufficientlylow partial pressures of CO₂ the extraction process will be limited byair-side resistance. For ambient air in a packed column-type system(Tepe, J. B. and Dodge, B. F., Absorption of Carbon Dioxide by SodiumHydroxide Solutions in a Packed Column, Trans. Am. Inst. Chem. Engrs.,39, 255 (1943)), CO₂ absorption rates have been determined to beproportional to G^(α), where G is the air flow rate and the coefficientα varies from 0.35 at low flow rates to 0.15 at high flow rates.(Spector, N. A. and Dodge, B. F., Removal of carbon dioxide fromatmospheric air, Trans. Am. Inst. Chem. Engrs., 42, 827-48 (1946)). Thissuggests that at low CO₂ concentrations, such as 0.031%, the liquid sideresistance to transport ceases to be dominant. It is likely that inthese experiments, fluid surface regeneration was sufficiently fast toprevent a built up of liquid-side flow resistance.

The advantage of using a strong hydroxide for CO₂ capture is a high loadcapacity and a fast reaction time. The removal of CO₂ from air can beaccomplished by a system that will be limited by transport resistance inthe air side of the air-liquid contact surface. In a regime where thedominant transport resistance is on the air side, it is possible toestimate the size of the CO₂ extractor by the air drag the extractorcauses on the flow. Apart from the pressure gradient driven momentumflow, momentum transfer to the wetted surface follows a similartransport equation as the CO₂ diffusion. As a consequence, a system thatincurs a pressure drop roughly equal to ρv², which extracted virtuallyall of the initial momentum, will be able to extract a substantialfraction of the CO₂ from the flow. To set the scale of the operation, at10 m/s, the air flow through an opening of 1 m² carries a CO₂ load thatequals the CO₂ produced by generating 70 kW of heat from coal (LacknerK. S. et al., Carbon dioxide extraction from air: is it an option,Proceedings of the 24^(th) Annual Technical Conference on CoalUtilization and Fuel Systems, (1999)). A 100 MW power plant operating at33% efficiency would require 9,000 m² of wind cross section, if CO₂collection efficiency is to be about 50%.

Causticization: Causticization refers to the transformation of sodiumcarbonate into sodium hydroxide. It is generally performed by addingsolid calcium hydroxide to the sodium carbonate solution. The solubilityof calcium hydroxide is such that an emulsion is formed according toreaction (5):Na₂CO_(3(aq))+Ca(OH)_(2(s))→2NaOH_((aq))+CaCO_(3(s))  (5)

This reaction can also be written in its ionic form as follows:CO₃ ²⁻+Ca(OH)_(2(s))→2OH⁻+CaCO_(3(s))  (6)ΔG°=−18.2 kJ/mol (ΔH°=−5.3 kJ/mol)This process step regenerates the sodium sorbent. The CO₂ is removed asa solid through a filtration process. Lime, which would slakeimmediately in the aqueous solution, could be used as a startingmaterial; however, in air extraction, it is important recover the heatof the slaking reaction at elevated temperatures. Thus, the slaking stephas been separated from causticization.

Causticization rate has been shown to increase with temperature. Theinitial sodium carbonate concentration for those experiments was 2.0mol/l and the samples were subjected to constant stirring. Reaction (5)eventually approaches equilibrium and causticizing efficiency isgenerally in the range of 80 to 90%. Causticizing efficiency refers tothe amount of sodium carbonate converted to sodium hydroxide. It hasbeen determined that the rate constant for reaction (5) increased by afactor of 3 as the operating temperature was raised from 353 to 393K.(Dotson B. E. and Krishnagopalan A., Causticizing Reaction Kinetics,Tappi Proceedings 1990 Pulping Conference, 234-244 (1990)). The rateconstant dropped when the feed solution contained sodium hydroxide. Theexperimental causticizing efficiency for pure sodium carbonate and amixture of sodium hydroxide and sodium carbonate were ˜94% and ˜85%,respectively. The rate constant for the causticization is driven by theconcentration of free Ca ions in solution. Highly alkaline solutionswill limit the availability of dissolved Ca⁺⁺ at any time andconsequently reduce the rate of conversion. Elevated temperatures andactive stirring reduce diffusional resistance and thus will increase therate of reactions.

The concentrations of all the calcium species have been found to remainessentially constant throughout the reactions due to their lowsolubility, thus suggesting that the efficiency and rate constants maychange if insufficient calcium is present. This occurrence has beenprevented by using a 10% stoichiometric excess of lime. However, such anexcess results in solid calcium hydroxide being entrained with thefiltrate, which can produce higher energy consumption in the lime kilndue to the dehydration reaction.

The concentrations of the various species, both sodium and calcium, havea profound effect on the quality of the resultant filtrate. It has beenobserved that the solid phase of calcite is unstable in pure NaOHsolution greater than 2 mol/l and easily converts to Ca(OH)₂ (Konno H.et al., Powder Technology, 123, 33-39 (2002)). These solids becomestable in a 1 mol/l NaOH solution containing at least 0.02 mol/l Na₂CO₃.This latter solution mixture suggests that for an initial sorbentconcentration of 1 mol/L, 96% of the hydroxide ions were converted tocarbonate according to reaction (2). The presence of Na₂CO₃ also reducesthe solubility of calcite. The solubility of Ca(OH)₂ is stronglydependent on the NaOH concentration and drops by a factor 4, to 5×10⁻⁴mol/l as the NaOH increases from 0 to 0.5 mol/l. Observations of theconcentrations of Ca²⁺ and NaOH during the reaction have shown that theCa²⁺ concentration dropped and the NaOH concentration increased as thereaction progressed. The initial Ca²⁺ concentration was 1×10⁻³ mol/l. Itwas also noted that the Ca(OH)₂ super-saturation ratio is the drivingforce for nucleation. In effect, these processes balance the solubilityof calcium hydroxide against the solubility of calcium carbonate. Thevalues for the dissociation constants are available in the literature(Snoeyink V. L. and Jenkins D., Water Chemistry, p. 295, John Wiley andSons, New York (1980)).[Ca⁺⁺][OH⁻]²<K_(OH)=10^(−1.49) mol³/l  (8)[Ca⁺⁺][CO₃ ²⁻]<K_(CO3)=10^(−3.22) mol²/l  (9)Given that the calcium concentration is the same in both (8) and (9),the carbonate concentration is solved as follows:[CO₃ ²⁻]=(K_(CO3)/K_(OH))×[OH⁻]²  (10)

Assuming a 1 molar sodium solution, the effect of calcium on the chargebalance can be neglected, and the sodium concentration must thereforebalance all the negative ions. If causticizing efficiency (ε) is definedas the ratio of hydroxide ions over sodium ions, the followingrelationship is obtained: $\begin{matrix}{ɛ = \left( {{2{\frac{K_{{CO}\quad 3}}{K_{OH}}\left\lbrack {O\quad H^{-}} \right\rbrack}} + 1} \right)^{- 1}} & (11)\end{matrix}$Thus, the stable solution suggested above (Konno et al.) would containapproximately 1 mol/l hydroxide ions, suggesting a theoreticalcausticizing efficiency of 96%, which is slightly higher than theexperimental value that has been obtained (Dotson B. E. andKrishnagopalan A., Tappi Proceedings 1990 Pulping Conference, 234-244(1990)). The difference is likely due to the omission of ionic activityin the calculations.

The experimental work discussed above provides a pathway for recoveringsodium hydroxide from sodium carbonate. In the process, the carbondioxide has been transferred into a solid form of calcium carbonate,which can be readily removed from the liquid. After washing and drying,it can be thermally decomposed. The causticization takes place in anemulsion of calcium hydroxide.

Calcination of Limestone: The final stage of the air extraction processis the recycling of the calcite precipitate. This is accomplishedthrough thermal regeneration or calcination. Lime and limestone areamong the oldest materials used, with the first recorded use in theEgyptian pyramids. There are three essential factors in the kinetics ofdissociation: the dissociation temperature, the duration of calcination,and the CO₂ in the surrounding atmosphere. The reaction is shown below:CaCO_(3(s))→CaO_((s))+CO_(2(g)) ; ΔH°=+179.2 kJ/mol  (12)The first quantification of the results of thermal decompositioninvolved a decomposition temperature of 1171K in a 100% CO₂ atmosphereat atmospheric pressure (Johnston J., J. Am. Chem. Soc., 32, p. 938(1910)). Current practices use lime kilns to dissociate the calcite;these kilns vary greatly in their performance. A very importantperformance metric for air extraction is the thermal efficiency, whichis the product of the theoretical heat requirement and the availableoxide content divided by the total heat requirement. The thermalefficiency refers to the proximity to the theoretical minimum heatrequirement as defined by reaction (12), available lime refers to theamount of inert material present, in this case 7%. This translates intoa total heat requirement of 3.03 MMBtu per ton of lime, or 4.5 GJ pertonne of CO₂. The thermodynamic minimum heat requirement of 4.1 GJ/tonneCO₂ can be calculated from the enthalpy value in reaction (12). Thepotential cost of air extraction will be dominated by reaction (12); anyimprovement regarding the above-mentioned kinetic factors (sorbents,causticization and calcination) will directly affect the cost of theproject. A lower dissociation temperature will require less heat input,as will a shorter duration of calcination and a lower CO₂ content in thesurroundings.

Air Extraction as Carbon Capture: This example relates to the capture ofCO₂ directly from the atmosphere in a cost effective manner. As such, abrief comparison with the industry standards provides a benchmark forfuture work. Sterically hindered amines (SHA) and MEA are considered tobe potential CO₂ capture technologies. They are regenerated using steamand their thermal energy requirements are 700 and 900 kcal/kg CO₂ forKS-2 and MEA, respectively. These values can be converted to 2.9 and 3.8GJ/tonne CO₂. In one instance 90% of the CO₂ generated by the powerplants was captured (Mimura T. et al., Development of energy savingtechnology for flue gas carbon dioxide recovery in power plant bychemical absorption method and steam system, Energy Convers. Mgmt., 38,S57-62 (1997)); thus, the remainder has to be mitigated by other means.An economic analysis of CO₂ capture using MEA obtained a cost of $50 pertonne of CO₂ avoided. The durability of the sorbent is also an importantcost factor.

The air extraction process encompasses hydrating or slaking theresulting lime. Generally lime is regenerated in the hydration process,thus a great reduction in capture efficiency from one cycle to the nextis not expected. The process of hydration is believed to proceed via themigration of water into the pores of the lime particle. The hydrationreaction, shown below, then takes place.CaO_((s))+H₂O_((l))→Ca(OH)_(2(s)) ΔH°=−64.5 kJ/mol  (13)

The hydration causes both expansion and the liberation of heat, which,in turn, causes the particle to split, exposing fresh surfaces andthereby reducing the effects of sintering. The inclusion of thisreaction in the carbonation process will likely alter the performanceand durability of the lime cycle, as will the lower temperatures ofreaction. Slaked lime undergoes dehydration at temperatures above ˜700Kunder ambient conditions. This defines the range of possible operatingtemperatures for the hydration process. Hydration is highly exothermicand can provide useful heat energy if it is performed efficiently athigh temperatures.

The feasibility of air extraction will depend on the overall costcompared with alternative removal technologies. The cost per unitremoval will further depend on the energy requirements, the durabilityof the sorbents, and costs external to the process. These external costscould include excessive water losses from the wet scrubbing. As thispart of the process will be in contact with the open atmosphere,evaporation can be expected. This can be minimized by adjusting thesorbent concentration, which varies the vapor pressure until it matchesthat of the ambient air. The thermophysical properties of sodiumhydroxide solution are known for a wide range of concentrations. Thecalcination reaction is likely the most energy intensive for the statedprocess. This highlights the need for efficient heat management withinthe system. Additionally, any significant lime degradation will rapidlyraise costs and CO₂ management issues. Lime make up will have to begenerated through the calcination process, thereby releasing CO₂. Thisadditional CO₂ will raise the cost of the process either throughlowering the net amount avoided or increasing the total amountsequestered.

Although the air contactors in the systems described herein can be muchlarger than the equivalent contact surfaces in a flue stack involvingMEA, their contribution to the total cost may be very small. Therecovery MEA sorbents require similar amounts of energy; in contrast, inthe present procedures and systems, because the air is clean andhydroxides are not subject to oxidative losses, the make-up costs arelow in a hydroxide system. Accompanying the air extraction of CO₂ is theefficient management of heat generation. The processes of this inventionwill maximize CO₂ capture while minimizing energy consumption.

EXAMPLE 2

A second example of a CO₂ capture process and system of the presentinvention is presented herein below. As described, the process andsystem involve the formation of sodium carbonate from sodium hydroxideand CO₂ from the air and the conversion of calcium hydroxide intocalcium carbonate. The calcium hydroxide is recovered by calcining thelimestone precipitate and then slaking it with water. Individualreactions related to the process and system, along with free energy orenthalpy values, are presented below; thermodynamic values are based onthose as conventionally known in the pertinent art.

(1) 2NaOH+CO₂→Na₂CO₃+H₂O; ΔH°=−171 kJ/mol

(2) Na₂CO₃+Ca(OH)₂→2NaOH+CaCO₃; ΔH°=57.1 kJ/mol

(3) CaCO₃→CaO+CO₂; ΔH°=179.2 kJ/mol

(4) CaO+H₂O→Ca(OH)₂; ΔH°=−64.5 kJ/mol

(5) CH₄+2O₂→CO₂+2H₂O; ΔH°=−890.5 kJ/mol

(6) H₂O_((l))→H₂0_((g)); ΔH_(vap)=41 kJ/mol@373K, 0.1 Mpa

In the system, sodium hydroxide, a caustic soda, is used as a sorbent.An aqueous solution can drip over internal surfaces in the filter systemand thus allow for the capture of CO₂ from the air that passes throughthe system. Once the sorbent solution has reached the bottom of thesystem, it is either re-circulated or removed from the system forrecycling. The purpose of a recycling plant is to strip the CO₂ from thespent sorbent and return fresh sorbent to the capture device. After theCO₂ has been stripped, it can be compressed and sent to a disposal site.

Overall Energy Balance:

In considering this system in terms of its energy balance, it can becompared with the basic reaction of forming carbon dioxide:C+O₂→CO₂ ; ΔG°=−394.4 kJ/mol or 9 GJ/tonneThe heat of this reaction is given per tonne (metric ton) of CO₂. Thecombustion processes that lead to the production of CO₂ typicallygenerate more heat, since nearly all of these processes involve not onlythe oxidation of carbon, but to a smaller or larger extent the oxidationof hydrogen. Heat of combustion values for carbonaceous fuels range fromabout 500 kJ/mole of C for coal to 890 kJ per mole of carbon for naturalgas (or 11.4 GJ/tonne of CO₂ for coal and 20.2 GJ/tonne of CO₂ formethane).

The regeneration of sodium hydroxide from sodium carbonate requires aninput of energy. The primary chemical reaction in this process is thethermal decomposition of calcium carbonate, reaction (3). The enthalpyof reaction (3) is 179.2 kJ/mol or 4.1 GJ/tonne of carbon dioxide. Thisis the theoretical minimum energy penalty required to recycle thesorbent. It would be equally possible to express numbers in terms oftonnes of limestone or tonnes of lime. For every tonne of carbon dioxidethat is freed from the sorbent, 2.3 tonnes of limestone enter thecalcination process and 1.3 tonnes of lime leave the kiln. The value of4.1 GJ/tonne of carbon dioxide is approximately 45% of the free energyreleased during the combustion of pure carbon. For natural gas thisnumber would drop to 21%.

A method involving sodium hydroxide with lime washing as a viablesolution to air capture provides a base system in which to identify andestimate cost. The viability of the sorbent recovery process will bejudged on the net carbon production and the cost per tonne of carbondioxide. In this Example, a preliminary evaluation has been performed inwhich various assumptions for losses and parasitic energy requirementswere made. For example, it would be advantageous to have the pumpingrequirements met through renewable sources. Although a conventionalcalciner system is not ideal for calcining calcium carbonate in an aircapture system due to the large amount of carbon dioxide that would beemitted to the atmosphere, several different approaches can obtain heatwithout carbon dioxide emissions. This Example embraces a membraneprocess that uses a mixed conductor membrane (MCM) to keep unused airseparate from the combustion products. The advantage to this system isthat the combustion occurs in an O₂/CO₂ environment, thereby producing apure stream of CO₂ rather than a mixture with N₂ and impurities. Inprinciple, transporting oxygen across a membrane in the present systemis analogous to the solid oxide fuel cell (SOFC). However, a solid oxidebased membrane system (SOMS) is expected to be substantially lessexpensive than a solid oxide fuel cell, which uses similar types ofmembranes as electrolytes. Fuel cells, in contrast to membraneseparators, must provide charge electrodes on the surfaces of thesedevices in order to carry the return current. In the membraneseparators, the electronic back current is in effect short circuitingthe cell.

Without wishing to be bound by theory, in a SOMS system as describedherein, the economic data for fuel cells will be used in determining acost estimate. If treated as simple heat generators, these fuel cellscould reach efficiencies of 80-85%; waste heat will be very valuable inthis process. A commercially available product is the PC25™ systemmanufactured by International Fuel Cells, LLC. This is a 200 kW fuelcell system that consumes 2100 cft/hr or 86 lbs/hr (39 kg/hr) of naturalgas. The rated efficiency is 87% with 37% being electrical and 50% beingthermal. The estimated installed cost is approximately $4500/kW with astart up cost of $15,000. Federal and state funding may be available andcould amount to $10001 kW15. These specifications are used for thecalculations as the first generation SOFC's are currently unavailableand the DOE's performance target is for second generation SOFC's. Themost important difference with the commercial PC25™ is that the MCM orSOFC would operate at temperatures in the 1200-1300K range, which issuitable for calcinations and better suited for heat exchange. Operatingcosts also depend greatly on the price of natural gas. Current NYMEXprices are approximately $5.501 million BTU 16, but more typical longtime averages have been around $3.00 per million BTU.

The specifications listed above can be scaled down to a separation plantthat has a thermal throughput of 100 kW, equal to a power plant of 80%percent efficiency that would provide electricity and waste heat. Theplant would have the characteristics listed in the Table 1. The primaryenergy is based on the free energy of methane combustion shown inreaction (5) above in this Example. TABLE 1 Specifications forFeasibility SOFC Power Station Specification PC25TM Feasibility SOFCRating 200 kW 100 kW Methane Throughput 39 kg/hr 16 kg/hr′7 PrimaryEnergy 17,140 GJ/yr 7,020 GJ/yr Installed Cost $4,500/kW_(e)$4,500/kW_(e) Total Cost $900,000 $450,000The size of the capture devices and their design will not impact thecost of recycling the sorbent because the volume of sorbent isindependent of the partial pressure. Thus, it was appropriate to costthe system beginning at the downstream end, or the calciner. This is areasonable procedure as the calciner station is the most expensive item.To maximize efficiency, it would be highly desirable to keep itoperating continuously. In view of this, overall values for efficiencyand availability, as well as parasitic energy requirements, have beenassumed. Parasitic energy refers to the energy required to operate allof the equipment aside from the calciner. For these calculations, theoverall efficiency was 80%, the availability was 99% and the parasiticrequirement was 1%. Given those values, the total available energy forcalcining is approximately 5,500 GJ/year. If the aforementioned 4.8GJ/tonne for the calcining is assumed, an annual CO₂ extraction of 1,150tonnes is arrived at. To check the assumption regarding the parasiticrequirement, a simple calculation was performed to estimate the energyinvolved in lifting the sorbent material through an air contactersystem. If it is assumed that the calcining occurs once per day and thesorbent solution concentration is 0.5 mol/l, then about 140 m³ ofsolution is required to be circulated. An additional assumption of a 30m pumping height produces a daily consumption of 0.04 GJ. Given a factor2 for inefficiencies, an annual consumption of 30 GJ or 0.5% isobtained.

As expected, variations in the fuel and fuel cell costs will affect thecost per tonne. Table 2 contains a simple sensitivity analysis in whichfuel and fuel cell costs are varied. The values in the table are costper tonne extracted. TABLE 2 Sensitivity Analysis Variables Cost per kWInstalled Fuel Cost Overall Efficiency $4500 $1500 $500 $5.50/MMBtu 80%68 46 39 90% 61 41 35 $3.00/MMBtu 80% 52 30 23 90% 46 27 20These values do not include the cost of sorbent replacement, roughly $2per tonne of CO₂ extracted. This could be compared with the estimatecosts using monoethanolamine (MEA) of approximately C37-50/tonne $,roughly $40-55 USD/tonne.

For sizing purposes, a daily material balance, in tonnes per day, hasbeen prepared. The balance assumes that the incoming limestone contains20% water, by volume. The fuel cell is assumed to absorb 50% of theoxygen from the airflow. There are no figures for the sodium hydroxideas it is recycled within the system. In order to maximize the energyefficiency of the process it will be necessary to minimize heat loss.This will require an energy inventory in order to determine the optimaluse of the heat produced by the process. The lime will be reacted withwater to form slaked lime, an exothermic process that occurs at 500° C.according to reaction (4).

For the initial calculations it is assumed that the input temperature is300 K and the fuel cell temperature is 1200 K. The theoreticalcalcinations temperature for calcium carbonate is approximately 1173K.The values for sensible heat reflect the energy consumed or released bychanging the temperature of the various material streams. These numberswere calculated by integrating formulae for the specific heat, CP, ofeach component. The specific heat data was obtained from the literature8.20. Four reactions occur in the process; the evaporation of water fromlimestone, the calcination of limestone, the combustion of methane, thehydroxylation of calcium oxide. A daily material and energy balance ispresented in Table 3. Energy consumed is positive and energy released isrepresented as a negative number, in parenthesis. TABLE 3 Daily Materialand Energy Balance Mass Temperature Energy Sensible Reaction (tonne)Start Finish (kJ/mol) (GJ) (GJ) Input CaCO₃ (s) 7.13 300 1200 169.7912.10 12.77 H₂O (l) 1.28 300 374 5.60 0.40 2.90 N₂ (g) 9.67 300 12003.72 1.28 O₂ (g) 3.10 300 1200 38.30 3.30 CH₄ (g) 0.38 300 1200 56.181.35 (21.37) Output CaO (s) 3.99 1200 800 (21.27) (1.52) CO₂ (g) 4.191200 374 (41.41) (3.95) N₂ (g) 9.67 1200 374 (3.57) (1.23) O₂ (g) 1.551200 374 (35.97) (1.55) H₂O (g) 0.86 1200 374 (32.08) (1.54) (1.95)Calcium Hydroxide H₂O (g) 1.28 374 800 15.53 1.11 Ca(OH)₂ 5.27 800 374(45.28) (3.23) (0.53) Total 6.53 (8.18) Grand Total (1.65)The first observation to be made is that the entire process is a netheat producer. However, there are no explicit losses built into thecalculations. If the absolute value of all the energy changes is summed,−72 GJ is obtained, meaning the system can tolerate loses of up to 2%.The input water is the water contained in the limestone plus the amountrequired for the hydroxylation of the lime.

Based on initial analyses, the cost of air contacting in an air contactsystem is expected to be small compared to the sorbent recycle system,which has been discussed herein above. The goal is to ensure theadequate supply of adsorbed carbon dioxide while keeping theinfrastructure as small as possible. Given that the density of carbondioxide is approximately 0.015 mol/m³, an exposed area of ˜20 m² with awind speed of 6 m/s and an efficiency of 50% would be suitable for thesystem.

Despite the low concentration of carbon dioxide in air and systemconstraints, there is no fundamental reason why carbon capture from airis not possible. The system presented in this Example will generateextra carbon dioxide, but has been designed such that this carbondioxide is not released to the environment. For the design presented inthis Example, the cost depends on the availability of solid densemembranes through which oxygen ions can diffuse. It is also affected bythe design of the fluidized bed. It is advantageous that the process isa net heat producer. It is also noteworthy that this design sequesters1,100 tonnes of carbon dioxide a year.

All patent applications, published patent applications, issued andgranted patents, texts, and literature references cited in thisspecification are hereby incorporated herein by reference in theirentirety to more fully describe the state of the art to which thepresent invention pertains.

As various changes can be made in the above methods and compositionswithout departing from the scope and spirit of the invention asdescribed, it is intended that all subject matter contained in the abovedescription, shown in the accompanying drawings, or defined in theappended claims be interpreted as illustrative, and not in a limitingsense.

1. A method of extracting or sequestering carbon dioxide, comprising: (a) dissolving a magnesium bearing silicate in an aqueous acid to form an acidic solution; (b) increasing the pH of the solution of step (a) to precipitate one or more magnesium components; and (c) carbonating the precipitated magnesium components from step (b) to bind carbon dioxide.
 2. A method of extracting or sequestering carbon dioxide, comprising: (a) dissolving a magnesium bearing silicate in an aqueous acid to form an acidic solution; (b) increasing the pH of the solution of step (a) to precipitate one or more magnesium components; (c) carbonating the precipitated magnesium components from step (b) to bind carbon dioxide; and (d) recovering ammonia gas and acid by thermal decomposition or by electrodialysis.
 3. The method according to claim 1 or claim 2, wherein the magnesium bearing silicate of step (a) comprises peridotite rock.
 4. The method according to claim 1 or claim 2, wherein the magnesium bearing silicate of step (a) is selected from serpentine or olivine.
 5. The method according to claim 1 or claim 2, wherein the aqueous acid of step (a) is selected from citric acid, acetic acid, chromic acid, sulfuric acid, orthophosphoric acid, oxalic acid, ammonium bisulfate, or a combination of two or more thereof.
 6. The method according to claim 1 or claim 2, wherein the pH of the acidic solution is less than or equal to about pH 4.5.
 7. The method according to claim 1 or claim 2, further comprising the step of neutralizing the acidic solution of step (a) with a neutralizing agent to precipitate iron and silicate prior to the precipitation of the one or more magnesium components.
 8. The method according to claim 7, wherein the neutralizing step comprises a neutralizing agent selected from ammonia or magnesium hydroxide.
 9. The method according to claim 7, wherein the pH of the neutralized solution is less than or equal to about pH
 8. 10. The method according to claim 1 or claim 2, wherein increasing the pH in step (b) comprises an ammonia-containing reagent.
 11. The method according to claim 1 or claim 2, wherein increasing the pH in step (b) comprises a reagent selected from NaOH, KOH, NH₃, NH₄OH, NH₄HCO₃, (NH₄)₂CO₃, Na₂CO₃, or a combination thereof.
 12. The method according to claim 10 or claim 11, wherein increasing the pH comprises a reagent that is carbonated prior to precipitating the one or more magnesium components.
 13. The method according to claim 10, wherein the ammonia-containing reagent is selected from ammonia, ammonium hydroxide, ammonium carbonate, or ammonium bicarbonate.
 14. The method according to claim 13, wherein the ammonia-containing reagent is selected from ammonium carbonate or ammonium bicarbonate.
 15. The method according to claim 12, wherein the reagent that is carbonated prior to precipitating the one or more magnesium components is an ammonia-containing reagent.
 16. The method according to claim 1 or claim 2, wherein the one or more magnesium components of step (b) is Mg(OH)₂.
 17. The method according to claim 1 or claim 2, wherein the one or more magnesium components of step (b) is Mg(CO)₃, or hydrated forms thereof.
 18. The method according to claim 1 or claim 2, wherein the one or more precipitated magnesium components is carbonated in step (c) in a gas solid reaction between magnesium components and carbon dioxide at elevated temperature.
 19. The method according to claim 18, wherein the temperature is about 300° C. to less than about 900° C.
 20. The method according to claim 18, wherein the temperature elevation is performed in an autoclave under pressure.
 21. The method according to claim 20, wherein the pressure is about 1 to about 50 atmospheres or greater.
 22. The method according to claim 1 or claim 2, further comprising following step (c): (i) washing the precipitated magnesium component to remove residual salt; and (ii) exposing the precipitated and washed magnesium component to carbon dioxide at elevated temperature and pressure.
 23. The method according to claim 22, wherein the elevated temperature comprises about 300° C. to 500° C. or above.
 24. The method according to claim 22, wherein the elevated pressure comprises about 1 to about 50 atmospheres.
 25. The method according to claim 22, wherein the precipitated magnesium component is magnesium hydroxide or magnesium oxide.
 26. The method according to claim 1, further comprising recovering ammonia gas and acid following step (c) by thermal decomposition or by electrodialysis.
 27. The method according to claim 2 or claim 26, comprising recovering ammonia gas and acid following step (c) by electrodialysis.
 28. The method according to claim 1 or claim 2, wherein carbon dioxide is extracted or sequestered from air.
 29. The method according to claim 1 or claim 2, wherein the acid of step (a) is present in an amount at least 10% in excess of a stoichiometric amount for neutralizing magnesium in the magnesium bearing silicate.
 30. A method of extracting, reducing, or sequestering carbon dioxide, comprising: (a) dissolving a magnesium bearing silicate in an aqueous acid to form an acidic solution; (b) increasing the pH of the acidic solution to remove dissolved silica and produce a dissolved magnesium component; (c) precipitating a solid magnesium component from the neutralized solution with an ammonia containing reagent, thereby producing an ammonium salt in the solution; (d) precipitating the ammonium salt from the solution; and (e) carbonating the precipitated magnesium component to sequester or reduce carbon dioxide from the air.
 31. The method according to claim 30, wherein, in step (d) the ammonium salt is precipitated by reducing the volume of the solution.
 32. The method according to claim 31, wherein the volume is reduced by at least about 33%.
 33. The method according to claim 31, wherein the volume is reduced by evaporation or membrane separation.
 34. The method according to claim 30, wherein the carbonating step (e) is performed at elevated temperature.
 35. The method according to claim 34, wherein the elevated temperature is about 300° C. to less than about 900° C.
 36. The method according to claim 35, wherein the elevated temperature results from autoclaving under pressure.
 37. The method according to claim 36, wherein the pressure is about 1 to about 50 atmospheres or greater.
 38. The method according to claim 30, further optionally comprising the step of recovering ammonia gas and acid following step (e).
 39. The method according to claim 38, wherein the recovered acid is solid and anhydrous.
 40. The method according to claim 38, wherein the ammonia gas and acid are recovered by thermal decomposition or by electrodialysis.
 41. A method for extracting, reducing, or sequestering carbon dioxide, comprising: (a) dissolving a magnesium bearing silicate in an aqueous acid to form an acidic solution; (b) increasing the pH of the solution of step (a) to neutralize the acid solution of step (a); (c) introducing an ammonia reagent selected from ammonium carbonate or ammonium bicarbonate into the solution of step (b) to precipitate magnesium carbonate or hydrated forms thereof; and (d) carbonating the ammonia to form ammonium carbonate or bicarbonate so as to bind carbon dioxide.
 42. The method according to claim 41, further comprising the step of recovering ammonia gas and acid following step (c) and prior to step (d).
 43. The method according to claim 41, wherein the magnesium bearing silicate of step (a) comprises peridotite rock.
 44. The method according to claim 41, wherein the magnesium bearing silicate of step (a) is selected from serpentine or olivine.
 45. The method according to claim 41, wherein the aqueous acid of step (a) is selected from citric acid, acetic acid, chromic acid, sulfuric acid, orthophosphoric acid, oxalic acid, ammonium bisulfate, or a combination of two or more thereof.
 46. The method according to claim 41, wherein the pH of the acidic solution is less than or equal to about pH 4.5.
 47. The method according to claim 41, wherein iron and silicate precipitate in the neutralized solution of step (b).
 48. The method according to claim 41, wherein the pH is increased using a neutralizing agent selected from ammonia or magnesium hydroxide.
 49. The method according to claim 41, wherein the pH of the neutralized solution is less than or equal to about pH
 8. 50. The method according to claim 41, wherein increasing the pH in step (b) comprises an ammonia-containing reagent.
 51. The method according to claim 41, wherein increasing the pH in step (b) comprises a reagent selected from NaOH, KOH, NH₃, NH₄OH, NH₄HCO₃, (NH₄)₂CO₃, Na₂CO₃, or a combination thereof.
 52. The method according to claim 50, wherein the ammonia-containing reagent is selected from ammonia, ammonium hydroxide, ammonium carbonate, or ammonium bicarbonate.
 53. A method for extracting, capturing, or sequestering carbon dioxide from air, comprising: and (d) releasing the captured carbon dioxide to a system for collection, storage, or transport (a) exposing the air to a solid sorbent material comprising a large absorption surface so as to saturate the sorbent material with carbon dioxide; (b) removing remnant air from the saturated sorbent material under reduced pressure; (c) condensing the carbon dioxide onto a cold surface to capture the carbon dioxide in solid form; and (d) releasing the captured carbon dioxide to a system for collection, storage, or transport.
 54. The method according to claim 53, wherein the solid sorbent material comprises material moving along surfaces exposed to air.
 55. The method according to claim 54, wherein the moving material is selected from beads, rods, fabric, or moveable objects comprising rough surfaces.
 56. The method according to claim 53, wherein the solid sorbent material is inert.
 57. The method according to claim 53, wherein the solid sorbent material is hydrophobic.
 58. The method according to claim 53, wherein the solid sorbent material is selected from activated carbon, activated alumina, silicalites, or zeolites.
 59. The method according to claim 53, wherein the carbon dioxide sorbent is a material coated with one or more different sorbents.
 60. The method according to claim 53, wherein step (b) is performed in a first vacuum chamber.
 61. The method according to claim 53, wherein step (c) is performed in a second vacuum chamber comprising a temperature colder than that of the first chamber.
 62. The method according to claim 53, wherein the cold surface of step (c) comprises a cold trap suitable for dry ice formation.
 63. The method according to claim 53, wherein solid carbon dioxide generated in step (c) is held in a confined volume and warmed so as to become a pressurized gas.
 64. The method according to claim 63, wherein captured carbon dioxide sublimates in a containment vessel.
 65. The method according to claim 63, wherein the carbon dioxide is released under high pressure for storage, collection, or transport.
 66. A cryogenic system for capturing carbon dioxide and recovering a solid sorbent, comprising: (a) a first chamber for housing a carbon dioxide-laden sorbent material and removal of carbon dioxide from said sorbent material; (b) a vacuum system for removing air from said first chamber and attachable thereto; and (c) a second chamber connected to said first chamber and comprising a temperature suitable for condensation and collection of carbon dioxide from said first chamber as solid carbon dioxide onto one or more surfaces of said second chamber, said second chamber comprising a reduced partial pressure of carbon dioxide relative to said first chamber.
 67. The system according to claim 66, wherein said temperature in said second chamber is about −80° C. to about −100° C. or lower.
 68. The system according to claim 66, wherein the pressure of the second chamber comprises about 0.001 psi.
 69. The system according to claim 66, wherein the sorbent material comprises silicalites, zeolites, activated carbon, activated alumina, or a combination thereof.
 70. The system according to claim 66, wherein the cold surfaces of the second chamber capture cold carbon dioxide as dry ice.
 71. The system according to claim 70, wherein the cold carbon dioxide is captured as dry ice from about 15 minutes to several hours. 